 //定义一个变量进行判断，默认false 非全屏状态
 var exitFullscreen = false
 // 全屏事件
 let tuichu=document.querySelector('.s');
 function handleFullScreen() {
 var element = document.documentElement;
 if (exitFullscreen) {
 if (document.exitFullscreen) {
  document.exitFullscreen();
 } else if (document.webkitCancelFullScreen) {
  document.webkitCancelFullScreen();
 } else if (document.mozCancelFullScreen) {
  document.mozCancelFullScreen();
 } else if (document.msExitFullscreen) {
  document.msExitFullscreen();
 }
 exitFullscreen = false
 } else {
 if (element.requestFullscreen) {
  element.requestFullscreen();
 } else if (element.webkitRequestFullScreen) {
  element.webkitRequestFullScreen();
 } else if (element.mozRequestFullScreen) {
  element.mozRequestFullScreen();
 } else if (element.msRequestFullscreen) {
  // IE11
  element.msRequestFullscreen();
 }
 exitFullscreen = true
 }
 }
 tuichu.onclick=function(){
     handleFullScreen();
 }